ByDidi Tang and Eugene Hoshiko, Associated PressDecember 6, 2013

A couple in protective masks walk under Shanghai smog Friday. China's financial hub suffered one its worst bouts of smog, bringing visibility down to a few dozen meters and obscuring the Shanghai skyline.

SHANGHAI — Shanghai authorities ordered schoolchildren indoors and halted all construction Friday as China's financial hub suffered one of its worst bouts of air pollution, bringing visibility down to a few dozen meters, delaying flights and obscuring the city's spectacular skyline.

The financial district was shrouded in a yellow haze, and noticeably fewer people walked the city's streets. Vehicle traffic also was thinner, as authorities pulled 30 percent of government vehicles from the roads. They also banned fireworks and public sporting events.

"I feel like I'm living in clouds of smog," said Zheng Qiaoyun, a local resident who kept her 6-month-old son at home. "I have a headache, I'm coughing, and it's hard to breathe on my way to my office."

Shanghai's concentration of tiny, harmful PM 2.5 particles reached 602.5 micrograms per cubic meter Friday afternoon, an extremely hazardous level that was the highest since the city began recording such data last December. That compares with the World Health Organization's safety guideline of 25 micrograms.

The dirty air that has gripped Shanghai and its neighboring provinces for days is attributed to coal burning, car exhaust, factory pollution and weather patterns, and is a stark reminder that pollution is a serious challenge in China. Beijing, the capital, has seen extremely heavy smog several times over the past year. In the far northeastern city of Harbin, some monitoring sites reported PM 2.5 rates up to 1,000 micrograms per cubic meter in October, when the winter heating season kicked off.

As a coastal city, Shanghai usually has mild to modest air pollution, but recent weather patterns have left the city's air stagnant. On China's social media, netizens swapped jokes over the rivalry between Shanghai and Beijing, saying the financial hub was catching up with the capital in air pollution.

The environmental group Greenpeace said slow-moving and low-hanging air masses had carried factory emissions from Jiangsu, Anhui and Shandong provinces to Shanghai. But it said the root problem lies with the excessive industrial emissions in the region, including Zhejiang province to the south.

"Both Jiangsu and Zhejiang should act as soon as possible to set goals to reduce their coal consumption so that the Yantze River Delta will again be green with fresh air," Huang Wei, a Greenpeace project manager, said in a statement.